(a) Schematic of all-silicon THz plasmonic metamaterial absorbers (PMAs). (b) Physical photograph of the PMAs. (c) SEM image of the designed PMAs. Inset: false color scanning electron micrograph of the lateral wall of the structure. The red part is the etched silicon, and the blue part is the silicon substrate. (e), (f) The absorption spectra of quad-band (e) and tri-band (d) PMAs, respectively. (f) The absorbance and reflectance spectrum of the fabricated absorber with experiment [22].